Metal pickling



252. COMPOSITIONS,

Patented Apr. 29, 1930 UNITED STATES Examiner PATENT oFFIcia JAMES C. 'V'IGNOS, OF NITBO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIES 00., OF AKRON,

OHIO, A CORPORATION OF OHIO METAL PICKLING Io Drawing.

The present invention relates to the cleaning and preservation of a metallic surface wherein the surface is in contact with hquids of an acid nature. More particularly, the 5 invention relates to the prevention of exces-;

sive pitting and over-pickling of metals when subjected to the pickling process. The 1nvent-ion includes the provision of a regulator or inhibitor for causing the acid of the pick ling bath to attack selectively unclean portions of metallic surfaces to the substantial exclusion of corrosive action on the clean portions of the metallic surfaces.

In the art of pickling, a metal is treated with a dilute acid to remove rust, scale and like deposits, after which the metal is washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid solution removes such deposits, but also attacks the cleaned metal itself. The action of the pickle liquor on the metal not only wastes valuable metal, but also uses up the strength of the acid which should be directed to removing rust, scale or other deposits.

By means of the present invention, the objectionable features of the pickling process are substantially overcome and eliminated. To accomplish this in accordance with the present invention, there is added to the pickling bath or other acid solution employed, a regulating agent or ingredient which acts to control the action of the acid in removing the scale, rust and the like, or in other words, it selectively removes oxides and the like without materially attacking the free metal.

The regulators or inhibitors which are disclosed in the present application comprise the reaction product of aldehydes and salts of the 40 arylisubstituted ditliibcarbamic acids. These \ragfi ators or inhibitors hereinbefore mentioned possess inggeneral the following formula.

1928. Serial K0. 271,118.

wherein R represents hydrogen or an organic ,-'f0rming group.

One of the preferred type of inhibitors, for example, the reaction product of acetaldehyde and ammonium phenyl dithiocarbamate was formed by reacting approximately two molecular proportions (372 parts) of ammonium phenyl dithiocarbamate and somewhat more than one molecular proportion of acetaldehyde in the presence of an organic solvent, for example ethyl alcohol, at a temperature of approximately below 10 C. Other members of the preferred type of compounds were prepared in a similar manner.

The invention will be readily understood from the following description and examples. In the examples set forth for carrying out the metal pickling process, conditions were imposed which duplicated as well as possible those commonly followed in commercial practice so far as concerned acid concentrations and temperatures employed. The heating of the metallic test strips in the pickling liquor, in the manner as hereinafter set forth was. however, from three to four times that ordinarily followed in practice for the acid concentrations employed.

Test pieces of steel approximately three inches square were cut from the sheets having a carbon content of approximately 0.04%, and 0.12% as hereinafter stated. These pieces were then immersed in approximately 500 cc. of sulfuric acid solution containing approximately 8% by weight of 66 Baum acid and a small quantity of one of the preferred type of inhibitors. Although the quantity of inhibitor used may vary between relatively wide limits, it has been found that particularly faw.

tration, commercial practice is to pickle at 100 approximately from 150 to 190 F. (66 to 88 C.), for from fifteen to twenty minutes. In all cases, blank tests were also carried out simultaneously with and similar in every respect to those described except that no inhibitor was added to the pickle liquor. After the pickling test had been completed, the test pieces were weighed and the loss in weight ascertained.

The reaction products of .aldghygles and salts of aryl substituted dithiodarbamie acids hereinbefo re'statedas effective for preventing excessive deterioration of metals immersed in or subjected to the action of an acid solutlon have been employed in the following manner.

A sulfuric acid solution was prepared in the manner hereinbefore stated and about 0.01 grams of the reaction product of approximately two molecular proportions of ammonium phenyl dithiocarbamate and somewhat more than one molecular proportion of acetaldehyde added thereto. The resulting solution contained about 0.002% by weight of the said reaction product. Iron test strips containing approximately 0.04% carbon were then immersed in the solution for about sixty minutes while maintaining the temperature thereof at approximately from 80 to 85 C. The loss in weight of the test strips resulting from the pickling treatment was found to be only about 4.2% of the loss that resulted when a similar test strip was pickled under the same conditions in an acid solution containing no inhibitor. In other words, the inhibitor decreased by about 23/24 the metal loss due to solvent action of the acid on the metal. hen this loss was calculated on the basis of the surface of the metal exposed to the solution, it was found to amount to approximately .00061 grams per square inch as compared with a loss of .0145 grams per square inch where no inhibitor was employed.

A similar test was made in which two test pieces of steel, each approximately three inches square and containing approximately 0.12% of carbon. were immersed in a sulfuric acid solution of the strength hereinbefore mentioned containing about 0.01 grams of the rgaptioi prgduct of ammonium phenyl dithiodarbamate and acetaldehyde. The loss in weight of the teststrips resulting from the pickling treatment was found to be only about 1.0% of the loss that resulted when similar test strips were pickled under the same conditions in an acid solution containing no inhibitor.

Other examples wherein an acid solution of the strength mentioned and which contained approximately 0.004% by weight of the preferred type of inhibitor, are shown in the following table. In these examples the steel test pieces contained approximately 0.04% of carbon.

The reaction product of aldehydes and salts of other aryl substituted dithiocarbamic acids may also be employed as inhibitors in the manner hereinbefore described.

As shown in the various examples hereinbefore set "forth, the reaction products of aldehydes and salts of the aryl substituted dithiocarbamic acids comprise a class of effective inhibitors .in processes wherein metals are subjected to the action of an acid. Greater inhibiting action has been found to be produced by the use of a larger quantity of the various products than that set forth in the examples. However, it is not desirable to use a greater quantity of inhibitor than will completely dissolve in the solution employed.

The examples hereinbefore set forth are to be understood as illustrative only and not at all limitative of the scope of the invention. Other examples of the processes described are apparent to those skilled in the art to which the invention pertains, wherein metals other than those particularly described may be similarly treated or different acids or acid concentrations may be employed, or the periods of treatment may be varied or different temperatures employed. The invention is to be considered as limited solely by following claims wherein the invention is claimed as broadly as possible in view of the prior art.

Whatis claimed is:

1. The process of cleaning a metal surface which comprises immersing such metal in a sulfuric acid solution containing a small proportion of the reaction product of an aldehyde and a salt of an aryl substituted dithiocarbamic acid.

2. The process of cleaning a metal surface which comprises immersing such metal in a sulfuric acid solution containing a small proportion of the reaction product of an aldelayde and a salt of phenyl dithiocarbamic ac1 3. The process of cleaning a metal surface which comprises immersing such metal in a sulfuric acid solution containing a small proportion of the reaction product of an aldehyde and ammonium phenyl dit-hiocarbamate.

4. The process of cleaning a metal surface which comprises immersing such metal in a sulfuric acid solutidmcontaming a small proportion of the reaction product of an aliphatic aldehyde and ammonium phenyl dithiocarbamate.

5. The process of cleaning a metal surface which comprises immersing such metal in a sulfuric acid solution containing a small proportion of the reaction product of metaldehyde and ammonium phenyl dithiocarbamate.

6. The process of cleaning a metal surface, which comprises immersing such metal in a sulfuric acid solution containing a small proportion of the reaction product of approximat-ely two mols of ammonium phenyl dithiocarbamate and somewhat more than one mol of acetaldehyde.

7. The process of cleaning a metal surface which comprises immersing such metal in a sulfuric acid solution containing a small proportion of an or anic compound obtained by combining an aliphatic aldehyde with a salt of an aryl substituted dithiocarbamic acid and possessing the following formula wherein R represents hydrogen or an organic radical and M represents a metal or a saltforming group.

8. A metal-treating compound comprising a sulfuric acid solution containing a small proportion of an organic compound obtained by combining an aliphatic aldehyde with a salt of an aryl substlt-uted dithiocarbamic acid and possessing the following formula n I i-C wherein R represents hydrogen or an organic radical and M represents a metal or a saltforming group.

9. A metal-treating compound comprising a sulfuric acid solution containing a small proportion of the reaction product of an aldehyde and a salt of an aryl substituted dithiocarbamic acid.

10. A metaLtreating compound comprising a sulfuric acid solution containing a'small proportion of the reaction product of an aldehyde and ammonium phenyl dithiocarbamate.

11. A metal-treating compound comprising a sulfuric acid solution containing a small proportion of the reaction product of acetaldehyde and ammonium phenyl dithiocarbamate.

12. The process of cleaning a metal surface which comprises immersing suchmetal in a sulfuric acid solution containing a small proportion of a reaction product of an aliphatic aldehyde and an alkali metal salt of a phenyl dithiocarhamic acid.

13. A metal treating compound comprising a sulfuric acid solution containing a small proportion of a reaction product 0 an aliphatic aldehyde and an alkali metal salt phenyl dithiocarbamic acid.

In testimony whereof I hereunto aifix my signature.

JAMES C. VIGNOS.

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